The four main intelligence agencies — the Central Intelligence Agency, the National Security Agency, the F.B.I. and the Office of the Director of National Intelligence — compiled the assessment, and a declassified version was released Jan. 6, 2017. It said that all four agencies had “high confidence” that Russian spies had tried to interfere in the election on the orders of their president, Vladimir V. Putin.

The statements by top committee members on Wednesday came after the panel held a closed hearing with the men who led the intelligence agencies when the assessment was conducted, including John O. Brennan, the former C.I.A. director, and James B. Comey, the F.B.I. director fired by Mr. Trump.

The committee’s finding on Wednesday is the second of four interim conclusions that the panel plans to release before it issues its final report, which will most likely take place this year. This month, the committee released its findings on election security, concluding that Russian hackers surveilled around 20 state election systems and were looking for ways to undermine confidence in the United States’ voting process.

The Senate committee’s findings appear unlikely to give Mr. Trump much to crow about, unlike a parallel investigation by the House Intelligence Committee. That inquiry ended abruptly last month when the Republicans on the panel issued their own report, absolving the Trump campaign of aiding Russia’s election meddling and describing contacts between Trump associates and Russian officials or their intermediaries merely as ill-advised meetings.

The report, which ran about 250 pages, instead took aim at what Republicans called the misjudgments of Democrats and others, even as Republicans sought to play down the seriousness of mistakes by or suspicions about the Trump campaign. They faulted aides to Mrs. Clinton for secretly paying for opposition research that included information from Russian sources, and castigated federal law enforcement and intelligence agencies for failing to counter Russian interference as well as for purported investigative abuses and allegedly damaging national security leaks.

Mr. Trump breathlessly seized on the report, writing on Twitter: “‘No evidence’ that the Trump Campaign ‘colluded, coordinated or conspired with Russia.’ Clinton Campaign paid for Opposition Research obtained from Russia- Wow! A total Witch Hunt! MUST END NOW!”

Democrats on the committee joined the fray with a nearly 100-page dissenting document, denouncing the Republicans’ report as little more than a whitewash. They said that the Republicans showed no inclination to pursue even the most obvious of leads, and refused to interview crucial witnesses. The eagerness of Trump campaign aides to accept offers of Russian assistance, they said, suggested “a consciousness of wrongfulness, if not illegality.”